Book/Dissertation / PhD Thesis

FZJ-2016-02521

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Development of Embedded Thermocouple Sensors for Thermal Barrier Coatings (TBCs) by a Laser Cladding Process

Zhang, Y. (Corresponding author)FZJ*

2016
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-129-3

Please use a persistent id in citations: http://hdl.handle.net/2128/11198

Abstract: Thermal barrier coatings (TBCs) are now being widely used on gas turbine engines to lower the surface temperatures of metallic substrate from extreme hot gas stream in combustor and turbine components. The thermally grown oxide (TGO) growth rate plays an important role in the lifetime of TBC systems. The accurate real-time monitoring of bond-coat/ 8YSZ interface temperature in thermal barrier coatings (TBCs) in hostile environments opens large benefits to efficient and safe operation of gas turbines. A new method for fabricating high temperature thermocouple sensors which can be placed close to this interface using laser cladding technology has been developed. K-type thermocouple powders consisting of alumel (Ni2Al2Mn1Si) and chromel (Ni10Cr) were studied as candidate feedstock materials. A thermocouple sensor using these materials was first produced by coaxial continuous wave (CW) or pulsed laser cladding process onto the standard yttria partially stabilized zirconia (7~8 wt.% YSZ) coated substrate and afterwards embedded with a second YSZ layer deposited by the atmospheric plasma spray (APS) process. The process parameters of the laser cladding were optimized with respect to the degradation of the substrate, dimensions, topography, thermosensitivity and embeddability, respectively. Infrared cameras were used to monitor the surface temperature of clads during this process. The manufacture of the cladded thermocouple sensors provides minimal intrusive features to the substrate. The dimensions were in the range of two hundred microns in thickness and width for CW laser cladding and less than 100 microns for pulsed laser cladding. Additionally, continuous thermocouple sensors with reliable performance were produced. It is possible to embed sensors manufactured by CW laser cladding rather than by pulsed laser cladding due to the limited bonding strength between the clads and the substrate. Periodically droplets were formed along the clads under improper parameters, the mechanism to this is discussed in terms of particle size distribution after interaction with the laser beam, melts duration and Rayleigh’s theory. To sum up, laser cladding is a prospective technology for manufacturing microsensors on the surface of or even embedded into functional coatings that can survive in operation environments for in-situ monitoring. Production of sensors within thermal barrier coatings (TBCs) increases the application field of the laser cladding technique.

Note: Ruhr-Universität Bochum, Diss., 2015

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 113 - Methods and Concepts for Material Development (POF3-113) (POF3-113)
2. HITEC - Helmholtz Interdisciplinary Doctoral Training in Energy and Climate Research (HITEC) (HITEC-20170406) (HITEC-20170406)

Appears in the scientific report 2016

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